1. Field of the Invention
The present invention relates to a transparent cover plate for preventing the surface reflection of the display screen of a display apparatus and, more particularly, to a glare-proof transparent cover plate capable of reflecting external incident light in a course deviating from the observer's line of vision to the screen.
2. Description of the Prior Art
Generally, the display screen of a display apparatus is covered with a transparent cover plate. When the transparent cover plate is a flat glass plate or a flat transparent synthetic resin plate, external incident light is reflected directly toward the observer along the line of vision of the observer, which dazzles the observer and interferes with the visibility of the display screen.
In order to solve such a problem, glare-proof transparent cover plates have been proposed. Japanese Provisional Patent Publication No. 56-133701 discloses a glare-proof transparent cover plate having a flat back surface and a corrugated front surface provided with parallel sawtooth ridges each having an inclined surface extending at an angle to the back surface and a horizontal surface extending perpendicularly to the back surface. This known transparent cover plate is capable of deflecting the reflection from the front surface thereof from the user's line of vision. However, this transparent cover plate is not provided with any measures to deal with the external light that penetrates the transparent cover plate. External light that penetrates the transparent cover plate is refracted by the transparent cover plate material and is reflected from the flat back surface of the transparent cover plate toward the observer to reduce the visibility of the display screen. Furthermore, in this known transparent cover plate, the light emitted from the spontaneous light emitting screen of a display apparatus or a display apparatus having an internal light source is reflected from the surfaces of the sawtooth ridges in the direction of the user's line of vision to make the surfaces of the sawtooth ridges glitter and/or the light emitted from the display screen of the display apparatus is reflected by the inner surfaces of the sawtooth ridges in the direction of the user's line of vision to duplicate the images displayed on the display screen, which also deteriorates the quality of the images.